1.4. Preconception Number 3: Bulges Are Similar to Elliptical
Galaxies

Bulges and ellipticals have traditionally been fit by the same surface
brightness profiles, the
de Vaucouleurs R1/4 law; for simplicity, one is
tempted to assume that bulges are
simply scaled-down ellipticals and that they formed the same way. N-body
simulations (e.g.
van Albada 1982),
together with analytic considerations of "maximum entropy" end states
(Tremaine et al 1986),
suggested that this was through violent relaxation of a
dissipationless, perhaps lumpy, system. These ideas incorporate the
proposition (e.g.
Toomre 1977,
Barnes & Hernquist
1992)
that equal-mass mergers destroy preexisting stellar disks and form bulges
and ellipticals, of which these latter two are distinguished only by mass.

Furthermore, the stellar kinematics of ellipticals and bulges of the
same luminosity are
similar, in that each rotates approximately as rapidly as predicted by
isotropic oblate models
(Davies et al 1983).
However,
the two general categories of "bulges" and "ellipticals" are
becoming clear to be somewhat heterogeneous and may cover systems that
formed in a variety of ways.

The above preconceptions may be tested against modern data. We proceed
with the
systems for which the most detailed data may be obtained, the galaxies
in the Local Group, and then outward in distance.